A resin layer having cholesteric regularity (hereinafter, it will be referred to as “cholesteric resin layer”) has a characteristic of reflecting a circular polarized light which is in a rotational direction that is the same as the direction of helical rotation of cholesteric regularity (hereinafter, the characteristic will be referred to as “selective reflection characteristic”). To produce an optically anisotropic body that serves a purpose, it is needed to separate a circular polarized light which is in a rotational direction depending on the purpose. To do this, it is needed to obtain cholesteric regularities in right- and left-handed helical rotational directions.
If it is possible to form a circularly polarized light separating sheet comprising a cholesteric resin layer having the selective reflection band in the near-infrared light wavelength range, of incident near-infrared light, the circularly polarized light separating sheet can reflect only the circularly polarized light of a specific wavelength. If cholesteric regularities in right- and left-handed helical rotational directions can be obtained, it becomes possible to obtain an infrared reflection thin film with a reflectivity of 100%, for example.
To form the cholesteric resin layer having the selective reflection band in the visible light wavelength range, various chiral agents have been studied.
For example, Patent Literature 1 discloses a chiral compound described by the formula (Z11—Y11-A11-O—CO—O-M11-Y12)r1Xa wherein A11 is a spacer; M11 is a mesogenic group; each of Y11 and Y12 is a chemical bond, —O—, —S—, —CO—O—, —O—CO—, —O—CO—O— or the like; r1 is 2 to 6; Xa is an r1-valent chiral group; and Z11 is (a1) at least one of these groups is a reactive group which can participate in a polyaddition reaction, (a2) at least two of these radicals are substituents carrying a reactive group which can participate in a polycondensation reaction, and Z11 is a hydrogen or an unreactive radical as long as the condition (a1) or (a2) is satisfied.
Patent Literature 2 discloses a chiral compound described by the formula (Z12—Y13-A12-Y14-M12-Y15)r2Xb wherein A12 is a spacer; M12 is a mesogenic group; each of Y13 to Y15 is a chemical bond, —O—, —S—, —CO—O—, —O—CO— or the like; r2 is 2 to 6; Xb is an r2-valent chiral group; and Z12 is (a3) at least one of these groups is a group with an isocyanate, isothiocyanate, thiirane, aziridine, carboxyl, hydroxyl or amino group, (b2) the other group or each of the other groups is an unreactive group or H.
Patent Literature 3 discloses a compound described by the formula (Z13—Y16-[A13]r3-Y17-M13-Y18-)r4Xc wherein A13 is a spacer; M13 is a mesogenic group containing two phenylene radicals which are unsubstituted or substituted via —O—, —CO—, —O—CO—O— or the like; each of Y16 to Y18 is a single bond, —O—, —S—, —CO—O—, —O—CO— or the like; Z13 is a polymerizable group; r3 is 0 or 1; r4 is 2 to 6; and Xc is a chiral group. In Patent Literature 3, a left-handed-helix-inducing compound is also disclosed.
Patent Literature 4 discloses a chiral dopant described by the formula Z14—Y19-(A14)r5-Y20-M14-Y21—Xd—Y22-(A15)r6-Y23—Z15 wherein each of A14 and A15 is a spacer with a C1 to C30 chain length; each of Y19 to Y23 is a chemical bond, —O—, —S—, —C(═O)—, —C(═O)—O—, —O—C(═O)—, —CH═CH—C(═O)—O—, —O—C(═O)—O— or the like; M14 is a mesogenic group; each of Z14 and Z15 is a C1 to C4 alkyl, a polymerizable group, a radical having a polymerizable group, or the like; Xd is a dianhydrohexitol group; and each of r5 and r6 is 0 or 1.
Patent Literature 5 discloses that the isosorbide derivative typified by the compound represented by the following formula is useful as a chiral dopant:
wherein each of Re and Rf is Ps-Sp-Xe, an unsubstituted alkyl group, an alkyl group which may be substituted by —O—, —S—, —NH—, —CO—, —COO—, —OCO— or the like, etc.; Ps is a polymerizable group; Sp is a spacer group or a single bond; and Xe is a single bond, —O—, —S—, —OCH2—, —CH2O—, —CO—, —COO—, —OCO—, —OCO—O—, —OCH2—, —CH2O— or the like.
However, many of the compounds disclosed in these literatures are right-handed-helix-inducing polymerizable chiral compounds and they are not left-handed-helix-inducing polymerizable chiral compounds. A left-handed-helix-inducing polymerizable chiral compound is exemplified only in Patent Literature 1; however, many of the polymerizable chiral compounds disclosed in this literature have no description regarding their helical twisting power (HTP) or have low HTP and thus have a problem of low solubility and compatibility.